Probably in the minority, but I never figure out what I need ahead of time. I just get a lot, so it's no wonder I end up with 10 yards of fabric to make a lap size quilt (and that doesn't include the backing because I like Fat Backs). What can I say. I fall in love with certain fabrics/certain colors and never want to be without.
Yesterday I was in a LQS and someone came in and got 6 inches of fabric. She said she screwed something up in her cutting. I've never bought only 6 inches of anything!